1. Field of the Invention
The present invention relates to an antiskid brake control system wherein when there is a tendency of a vehicle wheel to lock at the time of braking the vehicle, a brake pressure adjusting device is utilized to decrease a brake pressure, wherein when the revolution of the wheel has been restored due to such pressure reduction, the brake pressure is revived, and wherein these operations are repeated to prevent the wheel from coming into its lock state.
2. Discussion of Background
FIG. 5 is a drawing to help explain the operation of a conventional antiskid brake control system as disclosed in e.g. Japanese Examined Patent Publication No. 21859/1986. Referring to FIG. 5, the conventional antiskid brake control system detects the speed 101 of a vehicle wheel. The system decreases a brake pressure 104 if the deceleration 102 of the wheel has achieved given deceleration reference value .alpha..sub.0 or more, or if the slip ratio found based on the wheel speed 101 and vehicle speed 103 has achieved given slip ratio reference value S.sub.0 or more.
The conventional system holds the brake pressure 104 constant if the wheel deceleration 102 has achieved not greater than the deceleration reference value .alpha..sub.0, or if the wheel acceleration 102 has achieved a first acceleration reference value .alpha..sub.1 or more provided that the wheel slip ratio has achieved not smaller than the reference value S.sub.0. The system gradually increases the brake pressure if the wheel acceleration 102 has achieved value smaller than the first acceleration reference value .alpha..sub.1.
The system rapidly increases the brake pressure 104 if the wheel acceleration 102 has achieved a second acceleration reference value .alpha..sub.2 or above which is greater than the first acceleration reference value .alpha..sub.1.
In e.g. the cases wherein the road on which the vehicle is driving is significantly slippery, or the vehicle has driven from a dry road onto an iced surface, the conventional antiskid brake control system cannot prevent a tendency of a vehicle wheel to lock, or sufficiently revive the locked wheel even though the brake pressure is extremely low.
As explained, an adequate pressure varies from the conditions of road surface to the conditions of road surface. It is extremely difficult to obtain an adequate pressure-decreasing amount without considering the relationship between the conditions of road surface and the brake pressure.